In Britain and parts of northwest Europe,
House Sparrow Passer domesticus populations have declined
markedly in urban-suburban landscapes since the mid-1980s. Little is
known about the demographic mechanisms or environmental causes of these
population declines, although lack of winter seed has been implicated as
a cause of the decline in House Sparrow numbers on farmland. This study focused on
factors affecting nesting success and annual productivity of nesting
House Sparrows along an urban-suburban-rural gradient centred on the
city of Leicester, England. Chick diet (inferred from faecal remains),
habitat selection by foraging adults and over-winter survival were also
studied.

Data were collected during 2001-2003 from 9
study areas spread along the urbanisation gradient. Most sparrows in
most study areas nested in or close to domestic gardens. Counts of
territorial males declined by 28% between 2001 and 2003, with the
largest declines in rural villages (25%) and suburban fringe (16%) and a
small increase (4%) in the urban centre.

Annual productivity (the estimated number of
fledged young/pair/year) was 25% lower in suburban areas and 18% lower
in rural areas than that measured during a recent study of farmland
House Sparrows in Oxfordshire. The main cause of this lower productivity
was starvation of chicks, (usually the first 5-6 days after hatching)
during June and July.

Chicks were more likely to starve if their
diet contained a high proportion of vegetable material (mainly
supplementary food) or ants, and less likely to starve if their diet
contained a high proportion of spiders. The number of young sparrows
successfully fledging, and the aggregate chick biomass, per nesting
attempt were greater in home ranges containing relatively high
proportions of deciduous shrub, trees and grass, and relatively little
concrete. During June and July 2003, more young fledged from home ranges
containing a higher density of aphids. Dipteran prey (Tipulids and other
flies) constituted a higher proportion of the chick diet in rural
localities than in urban-suburban localities, while Homopteran prey
(mainly aphids) constituted a higher proportion of chick diet in
urban-suburban localities.

After allowing for effects of weather,
nestling body mass and condition were negatively correlated to local
levels of nitrogen dioxide air pollution. Since body mass at fledging is
known to be a good predictor of immediate post-fledging survival, I
predicted that the lower average body mass at fledging among suburban
broods (compared to rural broods) would result in lower survival during
the first 10 days after fledging (57% for suburban fledglings, compared
to 70% for rural fledglings). The combined effects of lower annual
productivity and lower predicted post-fledging survival in suburban
localities were large enough to result in rapid predicted population
decline, given plausible annual survival rates of adults and first-year
sparrows and no net immigration. Under the same set of assumptions,
productivity and predicted post-fledging survival were high enough in
rural localities to maintain and even increase adult population size.

Deciduous shrubbery, grassy areas and
concrete were the main summer foraging habitats of suburban and rural
House Sparrows, with trees being heavily utilised in 2003. Ornamental
and evergreen shrubs were strongly avoided by foraging sparrows.

Stable isotope ratios of nitrogen (d15N
scores) in chick feathers are proposed to constitute a useful integrated
measure of the quality of the chick diet.
d15N scores differed
markedly between the vegetable (2.7), herbivorous invertebrate (4.7-6.4)
and carnivorous invertebrate (7.1-7.7) components of chick diet.
d15N scores in
sparrow chick feathers averaged 7.7 suggesting that the average
d15N score of
ingested diet was approximately 4.7 (i.e. was probably dominated by
vegetable material and herbivorous invertebrates). Feather
d15N scores were
lower in home ranges containing relatively large areas of concrete and
evergreen vegetation, and were a positive predictor of chick growth rate
and body condition.

The data presented in this thesis suggest
that the abundance of invertebrate prey within home ranges of House
Sparrows breeding within suburban and rural garden habitats limits the
quantity and quality of chicks raised to fledging. The combined effects
of relatively high rates of chick starvation and low body masses at
fledging (and consequently low post-fledging survival) observed in
suburban localities are large enough to result in rapid population
declines. Invertebrate abundance in suburban areas is probably
determined, at least in part, by the availability of suitable habitat
including native deciduous shrubbery, tress and grassland. Although
there is no evidence that the abundance of key invertebrate prey have
declined in urban-suburban landscapes, such declines do provide a
plausible mechanism for the observed declines in urban-suburban House
Sparrow populations. Management techniques, which increase densities of
key invertebrate prey during summer, have the potential to increase the
annual productivity and possibly the breeding densities of House
Sparrows in urban-suburban landscapes.